Thermocouple heating



. March 16 1926. 1.576.772

P. M GAHAN THERMOCOUPLE HEATING ELEMENT Filed NOV. 2. 1920 ATTORNEY Patented M... '16, 1926.

UNITED STATES PTNT OFFICE.

PAUL MAGGAHAN, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR T0 WESTINGHOU SE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

THERMOCOUPLE HEATING ELEMENT.

Application filed November 2, 1920. Serial in. 421,254.

To all 107mm concern: 1

Be it knownthat I, PAUL MAoGAHaN,--a citizen of the United States, and a residelit of Pittsburgh, in the county of Alleghenyvide a heatingelernent, of the above indicatedcharacter, that shallnot require excessive heating; I A further object of myinvention is to provide a. heating element forge-thermocou le that shallembody a portion which wili heat to a greatendegree than the adjoining portions when traversed by an electric currentr i A further object of my-inv'enti'on-is to rovide a. heating element, of. the above in icated character, that shall embody a portion having a relatively low eoefiicientof thermal andelectrical-conductivity. I The heatin elements that have been heretofore used or thermocouples have been composed of conducting material having arelatively high. inherent ;resistance. In order to develop a s'ufiieiently' high temper- I ature at the-junction of the thermo-couple,

at a point intermediate the endsof the heating element, it has been necessary to overheat the heating element. Such overheating has often dama ed the heating element.

In order to o viate the necessity for overheating the element, and in order to con centrate the heat at that portion of the element near Which the thermocouple is disposed, I provide a heating element having the two end portions thereof plated with conducting material. having relatively low resistance to form two paths of relatively low resistance on each side of a predetermined portion of the strip at which the thermocouple is to be disposed. The middlepor tion, having no low resistance. conducting materal associated therewith, retains its in herently high value of resistance.

to electrical mcasuia Since the value of the resistance of each end portion, from the respective ends of the element to the port-ion at which the thermocouple is disposed, comprises a path of low resistance, a relatively small amount of heat is developed in the end portions. Similarly, since the middleportion of the heating element, at which the thermo-couple is. dis-' posed, comprises a high resistance material, considerable heat is developed in that portion. Heat is thus concentrated at the point where needed and there is produced a.more sensitive therm-o-couple, which, when used in connection with a meter, renders the meter more efiicient.

Figure 1 ofthe accompanying drawings is a diagrammatic View illustrating the connection to an electric circuit of a. device em-- bodying my invention.

Fig. 2 is a view, partially in elevation and partially in section, of a heating element embodying my invention, the heat gradient thereof being indicated diagrammatically.

Fig. 3 is a schematic view of a heating ele- 'ment as heretofore used, the heat gradient of such an' element being indicated diagrammatically. I v

Referring'to Fig. 1, a source 1 of electro motive force supplies-current to a circuit 2 that isto be measured by a thermal ammeter 3. The ammeter 3 comprises an indicating device 4 and a thermal unit 5. The thermal unit 5 comprises a heating element 6 and a thermo-couple 7 that are enclosed in an evacuatedvessel 8.

Referring to Fig. 2, the heating element 6 comprises a conducting member 9 having an inherently high value of resistance, two portions of which are plated or otherwise covered with conducting material 10 of relatively low resistance from the respective .ends of the element 9 to the portion 11,,in-

termediate the ends, that remains uncovered. The low resistance material 10' may comprise a covering of copper, silver or gold. or of any other conducting material havj ing a low 'coeflicient of resistance. As illustrated bythe dotted curve, the maximum value of the heat gradient, curve occurs at "the uncovered portion 11.

he reason for the form of the heat gradient curve that is illustrated in Fig. 3.2 is readily apparent since'the two end portions, that are covered by the low resistance material 10, respectively form paths of relatively low resistaniie. relatively small amount of heat is'therefore developed in' the two end portions in comparison 'with the amount of heat'that is developed in the middle portion 11.

' Referring to Fig. B iillfl] dotted curve shown therein illustrates the'heat gradient curve of heating elements that have been ployed to raise the temperature f of the thermo-couple junction.

Although .I have shown the device as applied to a thermal amm'eter, it'is, of

course, obvious that the heater-may be ap-' plied to" any thermal f measuring instru-y ment.

Also, I donot limit the heating element "embodying my-.. invention to the: specific fiorm that is-illustrated nor to the specific metals mentioned since it may be. /ar1ously modified Without departing from tlie. spirit the appendedclaims.

- I claim "as my invent1'on:-

f: 1. An article ofmanufactUre and-scope of the invention,-as set "ffortl therealongfrom each; terminal thereof to a position'spaced'from the fother coating -..to provide'a concentrated heat-zone spaced from .said terminals .betWeenZ-the'fcoatings. 2. Anarticle-of manufacture comprising "a composite element in the .form of an'e1 ongated strip or filament including a core of high-resista' nce conducting mat'erial and coverings of relatively low-resistance material on the major portions of the element at either side of a relatively short uncovered portionof the strip,

3. An. article of manufacture comprising:

v a single integralybody of' high-resistance an elongated element of higl1-r'esistan'c-e,c 11- ducting material I and two ti1be-like bodies of-"relatively lower resistance 'condu cti'ngf material surrounding the element and intimately engaging the. same. in slightly. spaced end-to-end' relation to each otherto provide a concentrated heat zone therebe-' sition intermediate the i substantially throughout the lengthfofthe composite element and elongated filamentary portions of relatively lowerconductlng ma- 'terial intimately joined thereto in spaced;

end-to-end relation to each other to provide a concentrated heat zone thcrebetween. 5. An articleof manufacturecomprising acomposite element constructed entirely in the form of a iila'mentarystrip -01 ement'; including a base portion of relatively high resistance conductinginaterial extend- "ing substantiallythroughoutflthe length of the composite element" and ,elongated' filamentary portions of relatively, lower con-' ducting material intimately.- joined thereto in spaced rend-toend relation to each other and-extending substantially to the outer ends of the composite-element to providea concentrated heat zone intermediate: the; ends-of the composite-element;

6." An' article of inanufacture comprise .inganelement of high-resistance conduct inglmaterial' and two tubular bodies of rela tively lower-resistance Jconducting material surrounding thema'jor portion of the ele- -meht'and'intimat'ely joined thereto in spaced end-to-end' relationto eachother to prozone 'therebetween at'a local position inter mediate the ends of the element. p i In testimony whereof, I have hereuntof subscribed my namethis27th day'of Octoher 1920. a

i PAUL MACGAHAN.

fvide; a": relatively "short concentrated heat 

